Indirect evidence suggests that dihydrodiol dehydrogenase (EC 1.3.1.20) prevents the formation of the diol-epoxides of polycyclic aromatic hydrocarbons (ultimate carcinogens) by oxidizing their trans-dihydrodiol precursors to the noncarcinogenic catechols. We have purified the dihydrodiol dehydrogenase from rat liver cytosol and have found it to be potently inhibited by the nonsteroidal anti-inflammatory drugs (NSAIDS) i.e. by the same low concentrations that would inhibit cyclooxygenase. This proposal will determine whether this enzyme plays a crucial role in the detoxification of chemical carcinogens and will investigate whether its inhibition by the "aspirin-like" drugs represents a mechanism by which the initiation of tumor formation is enhanced. We will determine whether the dehyrogenase preferentially oxidizes proximate carcinogens, i.e. the non-K region trans-dihydrodiols of phenanthrene, chrysene, 5-methyl chrysene and benzo[a]pyrene. Racemic (plus-minus) trans-dihydrodiol substrates will be used in these studies and the stereochemical course of the reaction will be elucidated by measuring the CD spectra of the unreacted enantiomers. The products of these dehyrogenation reactions will be vigorously identified as the corresponding catechols by trapping them as their diacetates. The ability of the NSAIDS to enhance chemical carcinogenesis will be examined. Thus we will test these drugs as inhibitors of the enzyme catalyzed detoxification reactions described. Using the Ames Test as an end point for diol-epoxide formation we will show that the purified enzyme reduces the mutagenicity of benzo[a]pyrene and that this effect can be reversed by micromolar concentrations of indomethacin. In related studies we will measure the levels of dihydrodiol dehydrogenase in sites of polycyclic aromatic hydrocarbon induced chemical carcinogenesis, e.g. the lung, testis and mammary gland of Sprague-Dawley rats and the lung, kidney and forestomach of C3H mice. We will determine whether the oxidation of trans-dihydrodiols in these tumor sensitive tissues is inhibited by the "aspirin-like" drugs. As a prelude to demonstrating that the co-administration of benzo[a]pyrene and indomethacin results in the enhanced initiation of skin tumors, skin of mice strains used in tumorgenicity studies will be screened for the presence of the indomethacin sensitive enzyme.